Coordinated satellite-terrestrial frequency reuse

ABSTRACT

A system and method of operation for efficiently reusing and/or sharing at least a portion of the frequency spectrum between a first satellite spot beam and a second satellite spot beam, and/or an underlay terrestrial network associated with a second satellite spot beam. The spectrum is efficiently reused and/or shared between respective spot beams and/or associated underlay terrestrial systems in a manner minimizes interference between the respective satellite and terrestrial systems.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/079,574, filed on Mar. 14, 2005 now abandoned, and entitledCoordinated Satellite-Terrestrial Frequency Reuse, which itself is acontinuation of U.S. application Ser. No. 09/918,709, filed on Aug. 1,2001 now U.S. Pat. No. 6,892,068, and entitled CoordinatedSatellite-Terrestrial Frequency Reuse, which claims priority from U.S.Provisional Application Ser. No. 60/222,605 filed on Aug. 2, 2000 andentitled System and Method of Satellite-Terrestrial Frequency Reuse,from U.S. Provisional Application Ser. No. 60/245,194 filed Nov. 3, 2000and entitled Coordinated Satellite-Terrestrial Frequency Reuse, and fromU.S. Provisional Application Ser. No. 60/250,461 filed on Dec. 4, 2000and entitled System and Method of Satellite-Terrestrial Frequency Reuse,each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to frequency assignment, reuseand/or sharing among communications systems having both a terrestrialand a satellite component (dual-mode) and, more particularly, to asatellite-terrestrial communications system and method of operationthereof that provides frequency assignment, reuse and/or sharing betweenthe respective portions of the satellite system and/or terrestrialunderlay systems associated therewith, while substantially reducinginterference therebetween.

2. Background Description

In satellite-terrestrial systems that reuse the same spectrum, there isa need to efficiently allocate at least a portion of the frequencyspectrum of, for example, a first satellite coverage area to, forexample, a terrestrial network associated with a terrestrial coveragearea. The present invention provides a system and method for efficientlyassigning, reusing and/or sharing the spectrum between satellite and/orterrestrial systems in a manner that facilitates efficient frequencyspectrum usage, while minimizing interference between the respectivesatellite and terrestrial systems. The present invention can also beapplied to multiple satellite systems as well, in addition to, orinstead of, terrestrial systems.

FIG. 1 shows a prior art satellite radiotelephone system, as shown inU.S. Pat. No. 6,052,586, incorporated herein by reference. As shown inFIG. 1, a satellite radiotelephone system includes a fixed satelliteradiotelephone system 110 and a mobile satellite radiotelephone system130. The fixed satellite radiotelephone system 110 uses a firstsatellite 112 to communicate with a plurality of fixed radiotelephones114 a, 114 b and 114 c in a first communication area 116.

Fixed satellite radiotelephone communication system 110 communicateswith the plurality of fixed radiotelephones 114 a-114 c using a firstair interface 118 (e.g., at C-band). Control of the fixed satellitesystem 110 may be implemented by a feeder link 122 which communicateswith a gateway 124 and the public switched (wire) telephone network(PSTN) 126.

The feeder link 122 may include communication channels for voice anddata communications, and control channels. The control channels areindicated by dashed lines in FIG. 1. The control channels may be used toimplement direct communications between fixed radiotelephones, as shownfor example between radiotelephones 114 a and 114 b. The controlchannels may also be used to effect communications between a fixedsatellite radiotelephone 114 c and a mobile radiotelephone or a wiretelephone via gateway 124 and PSTN 126. The feeder link 122 may use thesame air interface or a different air interface from the first airinterface 118.

Still referring to FIG. 1, mobile satellite radiotelephone system 130includes a second satellite 132 that communicates with a plurality ofmobile radiotelephones 134 a-134 d which are located in a secondcommunication area 136. Mobile satellite radiotelephone system 130communicates with mobile radiotelephones 134 using a second airinterface 138 (e.g., at L-band or S-band). Alternatively, the second airinterface 138 may be the same as the first air interface 118. However,the frequency bands associated with the two air interfaces willgenerally be different.

A feeder link 142 may be used to communicate with other satellite,cellular or wire telephone systems via gateway 144 and PSTN 126. As withfixed satellite system 110, the feeder link 142 may includecommunication channels shown in solid lines and control channels shownin dashed lines. The control channels may be used to establish directmobile-to-mobile communications, for example, between mobileradiotelephones 134 b and 134 c. The control channels may also be usedto establish communications between mobile phones 134 a and 134 d andother satellite, mobile or wire telephone systems.

As with the fixed satellite radiotelephone system 110, the mobilesatellite radiotelephone system 130 may employ more than one satellite132 and will generally communicate with large numbers of mobileradiotelephones 134. The fixed and mobile satellite radiotelephonesystem may also use a common satellite.

Still referring to FIG. 1, a congested area may be present in the mobilesatellite radiotelephone system 130 where a large number of mobileradiotelephones 134 e-134 i are present. As is also shown in FIG. 1,this congested area may be in an overlapping area 128 between firstcommunication area 116 and second communication area 136. If this is thecase, excess capacity from fixed satellite radiotelephone system 110 maybe offloaded to mobile satellite radiotelephone system 130.

Capacity offload may be provided by at least one fixed retransmittingstation 150 a, 150 b, that retransmits communications between the fixedsatellite radiotelephone system 110 and at least one of the mobileradiotelephones. For example, as shown in FIG. 1, first fixedretransmitting station 150 a retransmits communications betweensatellite 112 and mobile radiotelephones 134 e and 134 f. Second fixedtransmitting station 150 b retransmits communications between thesatellite 112 and mobile radiotelephones 134 g, 134 h and 134 i. Thefixed retransmitting station need not be located in an overlapping areaas long as it can retransmit communications between the fixed satelliteradiotelephone system in the first area, and the mobile radiotelephones.

The fixed retransmitting stations communicate with the satellite 112using first air interface 118. However they communicate with the mobileradiotelephones using the second air interface 138. Accordingly, fromthe standpoint of the mobile radiotelephones 134 e-134 i, communicationis transparent. In other words, it is not apparent to the mobileradiotelephones 134 e-134 i, or the users thereof, that communicationsare occurring with the fixed satellite radiotelephone system 110 ratherthan with the mobile satellite radiotelephone system 130. However,additional capacity for the mobile satellite radiotelephone system 130in the congested areas adjacent the fixed retransmitting stations 150may be provided.

As shown in FIG. 1, a mobile radiotelephone can establish acommunications link via the facilities of the fixed satelliteradiotelephone system, even though the mobile radiotelephone isdesigned, manufactured and sold as a terminal intended for use with themobile satellite radiotelephone system. One or more operators may offerboth mobile and fixed telecommunications services over an overlappinggeographic area using two separate transponders in separate satellitesor within the same “hybrid” satellite, with one transponder supportingmobile satellite radiotelephones and the other supporting fixedsatellite radiotelephones. As capacity “hot spots” or congestiondevelops within certain spot beams of the mobile radiotelephone system,the fixed system, with its much higher capacity, can deploy fixedretransmitting stations to relieve the capacity load of the mobilesystem.

FIG. 2A shows a seven-cell frequency reuse pattern which may be used bythe mobile satellite radiotelephone system 130. Within each of therelatively large mobile system cells, each typically being on the orderof 400-600 kilometers in diameter, frequencies used by adjacent cellsmay be locally retransmitted by the retransmitting station at reduced,non-interfering power levels, and reused as shown in FIGS. 2B and 2C,thus substantially increasing the effective local capacity.

Accordingly, fixed retransmitting stations, located within the fixedsystem's footprint or coverage area, receive signals from the fixedsatellite and retransmit these signals locally. Frequency translation tobring the signals within the mobile system's frequency band willgenerally be provided. In the reverse direction, the fixedretransmitting stations receive signals from mobile radiotelephones andretransmit signals from the mobile radiotelephones to the fixedsatellite system. Again, frequency translation to bring the signalswithin the fixed system's frequency band will generally be provided.

The mobile radiotelephones are ordinarily used with the mobile satellitesystem. Accordingly, the fixed satellite system may need to beconfigured to support the air interface used by the mobile satelliteradiotelephone system.

Alternatively, if different air interfaces are used by the fixed andmobile satellite radiotelephone systems, the fixed retransmittingstation can perform a translation from one air interface to the other,for example, by demodulation and remodulation. The fixed retransmittingstation then becomes a regenerative repeater which reformatscommunications channels as well as control channels. However, if themobile and fixed systems both use substantially the same air interface,then the fixed retransmitting station can function as a non-regenerativerepeater.

One embodiment may use the simplest fixed retransmitting station byhaving the fixed and mobile systems both utilize the same air interfacestandard. Alternatively, the fixed system is configured to support themobile system air interface even though the fixed system may be usinganother air interface for fixed radiotelephone service.

FIG. 3 is another prior art system as shown in U.S. Pat. No. 5,995,832.FIG. 3 provides an overview of a communications system 310 showing thefunctional inter-relationships of the major elements. The system networkcontrol center 312 directs the top level allocation of calls tosatellite and ground regional resources throughout the system. It alsois used to coordinate system-wide operations, to keep track of userlocations, to perform optimum allocation of system resources to eachcall, dispatch facility command codes, and monitor and supervise overallsystem health. The regional node control centers 314, one of which isshown, are connected to the system network control center 312 and directthe allocation of calls to ground nodes within a major metropolitanregion. The regional node control center 314 provides access to and fromfixed land communication lines, such as commercial telephone systemsknown as the public switched telephone network (PSTN). The ground nodes316 under direction of the respective regional node control center 314receive calls over the fixed land line network, encode them, spread themaccording to the unique spreading code assigned to each designated user,combine them into a composite signal, modulate that composite signalonto the transmission carrier, and broadcast them over the cellularregion covered.

Satellite node control centers 318 are also connected to the systemnetwork control center 312 via status and control land lines andsimilarly handle calls designated for satellite links such as from PSTN,encode them, spread them according to the unique spreading codesassigned to the designated users, and multiplex them with othersimilarly directed calls into an uplink trunk, which is beamed up to thedesignated satellite 320. Satellite nodes 320 receive the uplink trunks,frequency demultiplex the calls intended for different satellite cells,frequency translate and direct each to its appropriate cell transmitterand cell beam, and broadcast the composite of all such similarlydirected calls down to the intended satellite cellular area. As usedherein, “backhaul” means the link between a satellite 320 and asatellite node control center 318. In one embodiment, it is a K-bandfrequency while the link between the satellite 320 and the user unit 322uses an L-band or an S-band frequency.

A “node” is a communication site or a communication relay site capableof direct one or two-way radio communication with users. Nodes mayinclude moving or stationary surface sites or airborne or satellitesites.

User units 322 respond to signals of either satellite or ground nodeorigin, receive the outbound composite signal, separate out the signalintended for that user by despreading using the user's assigned uniquespreading code, de-modulate, and decode the information and deliver thecall to the user. Such user units 322 may be mobile or may be fixed inposition. Gateways 324 provide direct trunks that is, groups ofchannels, between satellite and the ground public switched telephonesystem or private trunk users. For example, a gateway may comprise adedicated satellite terminal for use by a large company or other entity.In the embodiment of FIG. 3, the gateway 324 is also connected to thatsystem network controller 312.

All of the above-discussed centers, nodes, units and gateways are fullduplex transmit/receive performing the corresponding inbound (user tosystem) link functions as well in the inverse manner to the outbound(system to user) link functions just described.

Referring now to FIG. 4, which is another embodiment as shown in U.S.Pat. No. 5,995,832, a block diagram of a communications system 440 whichdoes not include a system network control center 312 is presented. Inthis system, the satellite node control centers 442 are connecteddirectly into the land line network as are also the regional nodecontrol centers 444. Gateway systems 446 are also available as in thesystem of FIG. 3, and connect the satellite communications to theappropriate land line or other communications systems. The user unit 322designates satellite node 442 communication or ground node 450communication by sending a predetermined code. Alternatively, the userunit could first search for one type of link (either ground orsatellite) and, if that link is present, use it. If that link is notpresent, use the alternate type of link.

The specification of U.S. Pat. No. 5,995,832 states that “[m]measuresincorporated in the invention to maximize bandwidth utilizationefficiency include the use of code division multiple access (CDMA)technology which provides an important spectral utilization efficiencygain and higher spatial frequency reuse factor made possible by the userof smaller satellite antenna beams. In regard to power efficiency, whichis a major factor for the satellite-mobile links, the satellitetransmitter source power per user is minimized by the use offorward-error-correcting coding, which in turn is enabled by the aboveuse of spread spectrum code division multiple access (SS/CDMA)technology and by the use of relatively high antenna gain on thesatellite.”

The specification of U.S. Pat. No. 5,995,832 also states that “[i]n asystem in accordance with the invention, the cluster size is one. Thatis, each cell uses the same, full allocated frequency band. This ispossible because of the strong interference rejection properties ofspread spectrum code division multiple access technology (SS/CDMA).”With regard to determining the position of user units 322, thespecification of U.S. Pat. No. 5,995,832 states that “[a]ccurateposition determination can be obtained through two-dimensionalmulti-lateration. Each CDMA mobile user unit's transmitted spreadingcode is synchronized to the epoch of reception of the pilot signal fromits current control site, whether ground or satellite node.”

However, in contrast to the prior art systems described, for example, inFIGS. 1-4, the present invention does not utilize in one embodimentfrequency translation between fixed and mobile systems. In addition, thepresent invention provides, for example, a robust satellite-terrestrialfrequency assignment and/or reuse scheme in another embodiment. Further,the present invention optionally utilizes a first frequency as adownlink frequency between a satellite and a first fixed and/or mobileuser terminal and as an uplink frequency between a second fixed and/ormobile user terminal and a base station, and a second frequency as anuplink between the first fixed and/or mobile user terminal and thesatellite and as a downlink between the base station and the secondfixed and/or mobile user terminal. Finally, the present invention is notlimited, for example, to the use of CDMA technology. Other advantagesand features of the invention are described below, that may be providedindependently and/or in one or more combinations.

SUMMARY OF THE INVENTION

It is a feature and advantage of the present invention to provide, forexample, a satellite-terrestrial communication system and method ofoperation thereof that facilitates efficient spectrum assignment, usage,sharing, and/or reuse.

It is another feature and advantage of the present invention to provide,for example, a satellite-terrestrial communications system and method ofoperation thereof that minimizes interference between the satellite andterrestrial systems.

It is still another feature and advantage of the present invention toprovide, for example, a satellite-terrestrial communication system andmethod of operation thereof that enables at least a portion of thefrequencies associated with an area of coverage to be utilized by aterrestrial system having overlapping coverage with a second area ofcoverage.

It is yet another feature and advantage of the present invention toprovide, for example, a satellite-terrestrial communications system andmethod of operation thereof that enables a terrestrial underlay systemassociated with a first area of coverage to reuse and/or share in asubstantially central portion thereof at least a portion of thefrequency spectrum of one or more adjacent areas of coverage of thesatellite system.

It is another feature and advantage of the present invention to provide,for example, a two system communication system wherein frequenciesassociated with a central portion of a first area of coverage for afirst communication system are assigned, reused and/or shared in asecond area of coverage associated with a second communication system.

It is another feature and advantage of the present invention to enable,for example, assignment, reuse and/or reassignment of satellite uplinkand downlink channels in a non-paired manner.

It is another feature and advantage of the present invention to provide,for example, a method by which the size of satellite spot beams and/orterrestrial cell sizes can be determined.

It is another feature and advantage of the present invention to, forexample, invert the frequencies between the satellite system and anunderlay terrestrial system, whereby a first frequency is used, forexample, as a downlink frequency between a satellite and a first fixedand/or mobile user terminal, and as an uplink frequency between a secondfixed and/or mobile user terminal and a base station. In addition, asecond frequency is used, for example, as an uplink between the firstfixed and/or mobile user terminal and the satellite and as a downlinkbetween the base station and the second fixed and/or mobile userterminal.

The present invention optionally provides both a terrestrial frequencyassignment and/or reuse plan, and a satellite frequency assignmentand/or reuse plan.

In one embodiment of the present invention, a first spot beam or set ofspot beams can reuse in a substantially central portion orpre-designated portion thereof, at least a portion of the frequencyspectrum of one or more adjacent or nearby spot beams. The remainingportion of the spot beam is partitioned into, for example, a number ofsubstantially equal sized subareas/subcells (hereinafter “subareas”)extending radially from approximately the periphery of the centralportion to or substantially to the spot beam boundary. Each of thecentral portions and the subareas will generally, although notnecessarily, comprise one or more terrestrial cells. In addition, theterrestrial cells may cover at least a portion of one or more subareasand/or spot beams. Other configurations of subareas may also be used.The number of subareas is optionally equal to the number of adjacentcells or spot beams. For example, in a cluster size of seven, the centercell or spot beam will comprise a substantially central portion and sixsubstantially equal size subareas, whereas in a cluster size of four,the cells or spot beams will comprise a substantially central portionand three substantially equal sized subareas. Any number of subareas,however, may alternatively be used.

In another embodiment, the spot beam channels selected for terrestrialassignment and/or reuse are optionally selected beginning with the spotbeam(s) farthest or substantially farthest away from the subarea of thespot beam under consideration, and proceeding to the spot beams closest(e.g., adjacent to) the spot beam subarea under consideration. Thesystem and method of the present invention in this embodiment thereforegenerally maximizes the separation between the satellite frequenciesthat are reused terrestrially within the terrestrial cells.

In accordance with another embodiment of the invention,satellite-terrestrial frequency assignment and/or reuse utilizes theinter-spot beam isolation (e.g., the isolation between the various spotbeams). Thus, the terrestrial system associated with a particular spotbeam and/or one or more subareas within a spot beam and/or one or moreterrestrial cells preferably use satellite channels that are notutilized by the spot beam since the spot beam provides an isolation thatcan be utilized in reducing interference. In other words, one aspect ofthe present invention takes the co-channel, co-beam interference and“transfers” it to co-channel, adjacent beam interference.

This feature of the present invention advantageously minimizesinterference between adjacent satellites/spot beams and adjacent cells.The transmissions by the terrestrial network(s) will generally, to acertain extent and depending on the local attenuation, be “heard” by theassociated satellite.

It should be understood that the present invention can utilize and/or bedeployed with all satellite (e.g., low-Earth orbit (LEO), mid-Earthorbit (MEO), geosynchronous orbit (GEO), etc.) and cellular terrestrialtechnologies (e.g., time division multiple access (TDMA), code divisionmultiple access (CDMA), Global System for Mobile Communications (GSM),etc.). The present system may also assign, share and/or reusefrequencies of other domestic, foreign, and/or international satelliteand/or terrestrial systems, subject to, for example, national, foreign,and/or international government regulatory approval.

Additional aspects of the present invention relate to determining thesize of the satellite spot beam cells and/or terrestrial cells. Inaccordance with the present invention, satellite spot beams areoptionally sized by a 3 dB loss rule. Specifically, spot beam size isoptionally determined by locating points that are substantiallyequidistant from and have approximately a 3 dB loss vis-à-vis asubstantially or effective central portion of the spot beam havingmaximum gain (e.g., where received satellite signal strength ismaximum). Spot beams and/or terrestrial cells can also be sized by usingfor example, a bit error rate. For example, with voice communication,spot beams and/or terrestrial cells can be sized in accordance with abit error rate in the range of, for example, 10⁻² to 10⁻³. For datacommunications, spot beams and/or terrestrial cells can be sized inaccordance with a bit error rate in the range of, for example, 10⁻² to10⁻³. This approach may result, for example, in systems using differentprotocols and/or air interfaces (e.g., CDMA, GSM) having different sizedspot beams and/or terrestrial cells.

In accordance with the present invention, the size of the substantiallycentral portion of the spot beam where any/all channels of adjacent spotbeams can be reused is preferably equal to an area comprisingapproximately 25% of the spot beam. For example, if circle having radiusr is used to approximate the area associated with, for example, ahexagonal shaped spot beam in a seven cell configuration, the centralportion will be approximately equal to 0.5 r (of the circle), whichcorresponds to an area equal to 25% of the circle. Other percentages ofthe central portion and/or shapes of the cells may alternatively beused.

In another embodiment of the present invention, the central portion ofthe first cell is optionally omitted. The spot beams are insteadpartitioned into a number of substantially equal sized subareas, wherebyeach subarea can terrestrially reuse adjacent spot beam channels, exceptfor those channels associated with a spot beam adjacent to the subarea.

Specifically, within any given satellite spot beam, satellite spot beamchannels are used for satellite transmissions, whereas the terrestrialtransmissions within that spot beam preferably use all satellitechannels except those allocated to the present spot beam. That is,within any given satellite spot beam, the frequency channels used in afirst spot beam are preferably not used in the underlay terrestrialsystem associated with the first spot beam.

For example, an area of coverage by a satellite system may compriseseven spot beams, with each spot beam having nine channels. Thus, thesystem would have sixty three channels that could potentially beassigned, shared and/or reused between the satellite and the respectiveunderlay terrestrial systems or between satellite systems. The satellitemay use, for example, nine (9) of the channels, and the remaining fiftyfour (54) channels can therefore be allocated to one or more respectiveunderlay terrestrial systems associated with each respective spot beam.In such a system, the nine channels associated with, for example, afirst spot beam are preferably not utilized by the underlay terrestrialsystem associated with the first spot beam. The general concept is toefficiently allocate (e.g., based on demand) the total frequency band(e.g., sixty three channels) between the terrestrial and satellitesystems within each of the seven spot beams and each of the respectiveterrestrial underlay systems associated therewith, while minimizinginterference therebetween.

The system in accordance with the present invention enhances spectrumusage by allocating and/or reusing at least a portion of the spectrumof, for example, at least a first satellite spot beam to an underlayterrestrial system preferably associated with or having overlappingcoverage with, for example, at least a second satellite spot beam, asubarea thereof, and/or a terrestrial cell associated therewith. Thesatellite-terrestrial communications system of the present inventionalso minimizes interference between each of the respective satellite andterrestrial systems that assign, reuse or share a portion of thespectrum.

The present invention also provides a system and method for coordinatingan assignment and/or reuse plan between satellite spot beams. If onespot beam gets too congested, it can borrow frequency spectrum from oneor more other spot beams that have available capacity. The presentinvention thus provides different ways of assigning and/or reusing thesame frequencies, and uses that fact to allow one or more satellitechannel sets to be selected for terrestrial reuse within a terrestrialnetwork on a substantially non-interfering basis with the satellitesystem.

In general, in accordance with one embodiment of the invention, eachsatellite channel is subdivided into uplink and downlink portions, andtherefore, has respective uplink frequencies and downlink frequenciesassociated therewith. In a further aspect of the present invention, theuplink frequencies and downlink frequencies associated with a givenchannel do not have to be assigned pairwise. For example, the uplinkfrequencies of a first channel associated with spot beam A can beassigned or reused terrestrially in spot beam B, whereas and thedownlink frequencies of the first channel associated with spot beam Acan be assigned or reused terrestrially in spot beam C. Similarly,channels can also be assigned or reassigned for use in other spot beamsand/or other satellite systems. Similarly, the uplink frequencies of afirst channel associated with spot beam A can be assigned or reusedterrestrially in a first subarea and/or terrestrial cell, for example,of spot beam B. In addition, the downlink frequencies of the firstchannel associated with spot beam A can be assigned or reused, forexample, terrestrially in a second subarea and/or terrestrial cell of,for example, spot beam B. Similarly, channels can also be assigned orreassigned for user in other spot beams.

It should be understood that the present invention generally worksregardless of cluster size, how many spot beams there are, or how manychannels there are per spot beam. For example, a fourteen cell repeatpattern or other cell pattern for satellite and/or terrestrial systemscould provide additional separation between the terrestrial networks andthe satellite networks. However, the allocation of frequencies betweenthe terrestrial network and the satellite network should be managedefficiently. For example, a large repeat pattern satellite and a smallrepeat pattern terrestrial network may give rise to inefficient use ofspectrum on the satellite (unless, for example, there is sufficientexcess spectrum), which could render the satellite spectrally limitedrather than power limited.

In this regard, it will be realized that one optional technique that maybe practiced with the present invention is increasing the terrestrialfrequency reuse cluster size, which generally minimizes the interferencebetween the satellite and terrestrial systems. For example, atraditional GSM type of pattern utilizes four cells with three sectorseach. If instead, twenty-four channels, for example, are assigned acrossthe cells, then one site in eight would have the same frequency, asopposed to one site in four having the same frequency (as with thetraditional GSM pattern). Thus, the number of instances where the samefrequency exists has been halved, and the amount of energy on anindividual channel has also been reduced by half. In this example, theinterference between the satellite and terrestrial systems wouldtherefore be reduced by approximately 3 dB vis-à-vis the traditional GSMsystem.

Finally, an additional aspect of the present invention concernsinverting frequencies to minimize interference between the satellite andterrestrial systems. The frequency inversion technique involvesreversing the satellite down-link and satellite up-link frequencies tobecome the terrestrial up-link (“return-link”) and terrestrial down-link(“forward-link”) frequencies, respectively, as described below indetail.

In particular, one embodiment of the present invention provides a methodand system for at least one of assigning and reusing frequencies betweenone or more communication systems. The method preferably comprises thesteps of configuring a first satellite spot beam having a first set offrequencies associated therewith. The first spot beam comprises a firstsubstantially central portion and a first plurality of subareas, whereeach of the first plurality of subareas extend substantially from aperiphery of the first substantially central portion to or near acircumference of the first satellite spot beam. Each subarea generallycomprises one or more terrestrial cells, although not all subareas arenecessarily required to have terrestrial cells associated therewith. Asecond satellite spot beam is preferably similarly configured. Aterrestrial cell is configured within the first satellite spot beamhaving a third set of frequencies associated therewith. Finally, themethod includes the step of at least one of assigning, reusing andborrowing, by the terrestrial system, at least one of a portion of thesecond set of frequencies and a portion of the first set of frequenciesused in the first central portion, responsive to predetermined criteriaassociated with the third set of frequencies, including at least one ofassigning, reusing and borrowing at least one of the second set offrequencies when the second set of frequencies are at leastsubstantially geographically distant from the first satellite spot beam.

Another embodiment of the present invention provides a method and systemfor making a telephone call using a satellite-terrestrial communicationssystem that at least one of assigns and reuses frequencies between afirst satellite spot beam or spot beams and a second satellite spot beamor spot beams. A user utilizes a mobile terminal to dial a telephonenumber within an area of a first terrestrial cell located within orassociated with a first satellite spot beam. The terrestrial cell has afirst set of frequencies associated therewith. The first satellite spotbeam comprises a first substantially central or predesignated portion,and a first plurality of subareas, wherein each of the first pluralityof subareas extend substantially from a periphery of the firstsubstantially central or predesignated portion to substantially near acircumference of the first satellite spot beam. Each of the subareas maycomprise one or more terrestrial cells, which may at least partiallyoverlap with one or more spot beams and/or subareas. A second spot beamis configured, which can optionally be configured differently than thefirst spot beam. If the first set of frequencies can not be utilized toestablish a connection, then a connection is established between thefirst mobile terminal and the second terminal by at least one ofassigning, reusing and borrowing, by the first spot beam, at least oneof the second set of frequencies, responsive to predetermined criteriaincluding at least one of assigning, reusing and borrowing at least oneof the second set of frequencies when the mobile terminal issubstantially geographically distant from the second satellite spotbeam.

A third embodiment of the present invention provides a method and systemfor at least one of assigning and reusing frequencies. The methodcomprises the steps of configuring a first communications area having afirst set of frequencies associated therewith. The first communicationarea preferably comprises a first substantially central or predesignatedportion, and a first plurality of subareas, wherein each of the firstplurality of subareas extend substantially from a periphery of the firstsubstantially central portion or predesignated area to or substantiallynear a circumference of the first communications area. Each of thesubareas may comprise one or more terrestrial cells, which may overlapwith at least a portion of other spot beams and/or subareas. A secondcommunications area is preferably similarly configured. A thirdcommunications area, having a third set of frequencies associatedtherewith, is preferably configured within the first communicationsarea. Finally, the method includes the step of at least one ofassigning, reusing and borrowing, by the third communications area, atleast one of a portion of the second set of frequencies and a portion ofthe first set of frequencies used in the first central portion,responsive to predetermined criteria associated with the third set offrequencies, including at least one of assigning, reusing and borrowingat least one of the second set of frequencies when the second set offrequencies are at least substantially geographically distant from thefirst satellite spot beam.

A fourth embodiment of the present invention provides a system andmethod that involves assigning and reusing frequencies between one ormore communication systems. A first satellite spot beam is configuredhaving a first set of frequencies associated therewith. The first spotbeam preferably comprises a first substantially central portion and afirst plurality of subareas, wherein each of the first plurality ofsubareas extend substantially from a periphery of the firstsubstantially central portion to substantially near a circumference ofthe first satellite spot beam. A second satellite spot beam is similarlyconfigured. A terrestrial cell, having a third set of frequenciesassociated therewith, is configured within the first satellite spotbeam. Finally, the method involves the step of at least one ofassigning, reusing and borrowing, by the second satellite spot beam, atleast one of a portion of the third set of frequencies responsive topredetermined criteria, including at least one of assigning, reusing andborrowing at least one of the third set of frequencies associated withthe at least one terrestrial cell when the portion is at leastsubstantially geographically distant from the second set of frequencies.

A fifth embodiment of the present invention also provides a system andmethod that involves assigning and reusing frequencies between one ormore communication systems. A first satellite spot beam is preferablyconfigured having a first set of frequencies associated therewith. Thefirst spot beam comprises a first substantially central portion and afirst plurality of subareas. Each of the first plurality of subareaspreferably extend substantially from a periphery of the firstsubstantially central portion to or near a circumference of the firstsatellite spot beam. A second satellite spot beam, having a second setof frequencies associated therewith, is configured. The second spot beamcan optionally have a different configuration than the first satellitespot beam. A terrestrial cell, having a third set of frequenciesassociated therewith, is configured within the first satellite spotbeam. Finally, the method involves the step of at least one ofassigning, reusing and borrowing, by the terrestrial system, at leastone of a portion of the second set of frequencies and a portion of thefirst set of frequencies used in the first central portion, responsiveto predetermined criteria associated with the third set of frequencies,including at least one of assigning, reusing and borrowing at least oneof the second set of frequencies when the second set of frequencies areat least substantially distant from the first satellite spot beam.

A sixth embodiment of the present invention also provides a system andmethod of at least one of assigning and reusing frequencies between oneor more communication systems. A first satellite spot beam is configuredhaving a first set of frequencies associated therewith. The first spotbeam preferably comprises a first plurality of subareas, wherein each ofthe first plurality of subareas extend from a substantially center areaof the first satellite spot beam to substantially near a circumferenceof the first satellite spot beam in a fan-like manner to form the firstplurality of subareas. A second satellite spot beam, having a second setof frequencies associated therewith, is configured. The second spot beamcan optionally have a different configuration than the first satellitespot beam. At least one terrestrial cell having a third set offrequencies associated therewith is configured within the firstsatellite spot beam. Finally the method involves the step of at leastone of assigning, reusing and borrowing, by the terrestrial system, atleast one of a portion of the second set of frequencies and a portion ofthe first set of frequencies used in the first central portion,responsive to predetermined criteria associated with the third set offrequencies, including at least one of assigning, reusing and borrowingat least one of the second set of frequencies when the second set offrequencies are at least substantially geographically distant from thefirst satellite spot beam.

In at least some of the above-described embodiments, the first pluralityof subareas are substantially equal sized cells having a first size, andthe second plurality of subareas are substantially equal sized cellshaving a second size. The first and second size may be substantiallyequal, or different.

The second set of frequencies, in accordance with at least some of theabove-described embodiments, are substantially distant from the firstsatellite spot beam when they are at least one of assigned, reused andborrowed for use in those first plurality of subareas not sharing acommon boundary with the second satellite spot beam. The first set offrequencies, in accordance with at least some of the above-describedembodiments, that are used in the first central portion comprise atleast one of those frequency sets respectively associated with satellitespot beams adjacent to or near the first satellite spot beam.

Further, at least some of the above-described embodiments, optionallyassign, reuse and/or borrow frequencies based on prioritization rulessuch as, for example, the dynamic load and capacity constraints of cellsthat frequencies are taken from.

At least some embodiments of the above-described invention utilize asubscriber terminal positioned within the first central portion that canbe assigned, reuse and/or borrow use any of the respective set offrequencies associated with the at least one second satellite spot beam.For example, a subscriber terminal positioned within or near the firstcentral portion can be assigned, reuse and/or borrow use any of therespective set of frequencies associated with any spot beams adjacentand/or near the first satellite spot beam.

Further, at least some embodiments of the present invention include asubscriber terminal positioned within or near a subarea not sharing atleast a portion of a common boundary with the second satellite spotbeam. Such a subscriber unit can be assigned, reuse and/or borrow any ofthe second set of frequencies associated with the second satellite spotbeam.

In addition, at least some embodiments of the present inventionoptionally assign, reuse and/or borrow frequencies based onpredetermined criteria such as load balancing, maintaining a reserve offrequencies, and received signal strength interference.

At least some of the embodiments of the above-described inventionoptionally include a second terrestrial cell within the second satellitespot beam. The second terrestrial cell optionally has a fourth set offrequencies associated therewith. The second terrestrial cell at leastone of assigns, reuses and borrows at least one of the first set offrequencies and is the frequencies used in the second central portion,responsive to predetermined criteria associated with the fourth set offrequencies. The predetermined criteria optionally include at least oneof assigning, reusing and borrowing at least one of the first set offrequencies when the first set of frequencies are at least substantiallygeographically distant from the second satellite spot beam.

The first central portion and the second central portion of at leastsome of the above-described embodiments optionally compriseapproximately twenty five percent of the area covered by the firstsatellite spot beam and the second satellite spot beam, respectively.

Further, the first set of frequencies and the second set of frequenciesoptionally comprise a plurality of paired uplink and downlinkfrequencies. A downlink frequency of a frequency set can optionally beused in a first subarea of the first spot beam, and a corresponding oneof the uplink frequencies can optionally be reused in a second subareaof the first or second spot beam.

In accordance with at least some of the above-described embodiments, thearea of coverage of a spot beam comprises an area having a radiussubstantially equal to a distance from a center of the spot beam havinga substantially maximum signal strength to a distance from the center ofthe spot beam where the signal strength of the spot beam is attenuatedby approximately 3 dB. Further, the number of subareas is optionallyequal to a number of spot beams comprising a cluster minus one. Othernumbers of subareas can also be utilized.

Finally, one or more satellites can be used to configure the first andsecond spot beams. In communicating between a first subscriber terminaland a second subscriber terminal and/or other communication device, anetwork operations controller is preferably used to facilitateassignment, borrowing and/or reuse of frequencies between spot beams,communication areas, and/or terrestrial cells, central portions of spotbeams and/or communication areas, subareas associated with spot beams,communication areas and/or terrestrial cells, and/or terrestrial cellswithin subareas.

Finally, an embodiment of the present invention provides a terrestrialcommunication system that uses satellite uplink and downlinkfrequencies, where a terrestrial cell site produces a signal at asatellite uplink frequency that is transmitted to a terrestrial terminalunit. The terminal cell site receives a signal at a satellite downlinkfrequency that was transmitted by the terrestrial terminal unit.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described hereinafterand which will form the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of description and should not beregarded as limiting.

As such, those skilled in the art will appreciate that the conception,upon which this disclosure is based, may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

Further, the purpose of the foregoing abstract is to enable the U.S.Patent and Trademark Office and the public generally, and especially thescientists, engineers and practitioners in the art who are not familiarwith patent or legal terms or phraseology, to determine quickly from acursory inspection the nature and essence of the technical disclosure ofthe application. The abstract is neither intended to define theinvention of the application, which is measured by the claims, nor is itintended to be limiting as to the scope of the invention in any way.

These together with other objects of the invention, along with thevarious features of novelty which characterize the invention, arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and the specific objects attained by its uses,reference should be made to the accompanying drawings and descriptivematter in which there is illustrated preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art diagram of a satellite radiotelephone system;

FIGS. 2A, 2B and 2C are prior art schematic diagrams of frequency reusein the satellite radiotelephone systems shown in FIG. 1;

FIG. 3 is a diagram showing an overview of the principal elements ofprior art communications system;

FIG. 4 is an overview block diagram of another embodiment of the priorart communications system shown in FIG. 3;

FIG. 5 is an exemplary high level block diagram of a system that can useand/or be used to produce the frequency reuse schemes in accordance withthe present invention;

FIG. 6 is an exemplary illustration of how a base station can enhancenetwork coverage, particularly in an area having no line of sight path(or reduced line of sight path) with a satellite;

FIG. 7 is an exemplary high level block diagram illustrating anintegrated satellite-terrestrial system that can use and/or be used toproduce the frequency reuse schemes in accordance with the presentinvention;

FIG. 8 a shows a first exemplary embodiment of frequency reuse within aspot beam where frequencies from any or all surrounding spot beams canbe reused in a substantially central portion thereof;

FIG. 8 b shows a first exemplary embodiment of frequency reuse in aseven cell pattern;

FIG. 8 c shows a variation of the first exemplary embodiment wherein thespot beams are depicted as being circular;

FIG. 9 illustrates an exemplary method by which spot beam size can bedetermined in accordance with the present invention;

FIG. 10 shows an exemplary way of determining the size of a center areaof a spot beam where frequencies from any of one or more adjacent spotbeams can be reused;

FIG. 11 a shows a second exemplary embodiment of terrestrial frequencyreuse within a satellite spot beam;

FIG. 11 b shows a variation of the second exemplary embodiment whereinthe spot beams are depicted as being circular;

FIG. 12 shows an exemplary method by which frequencies can be allocatedin an area that does not have a full complement of spot beams;

FIG. 13 is an exemplary flowchart illustrating a preferred method ofreusing frequencies;

FIG. 14 is an exemplary flowchart illustrating a method by whichfrequencies can be assigned when they are equidistant from a cell orsubarea to which they are assigned;

FIG. 15 is an exemplary flowchart illustrating a method by whichfrequencies can be dynamically assigned;

FIG. 16 is an exemplary flowchart illustrating a method by whichfrequencies can be preemptively reassigned based on, for example, loadbalancing and/or capacity issues;

FIGS. 17 a and 17 b illustrate different exemplary cluster size andchannel number combinations that can be used in accordance with thepresent invention;

FIG. 18 shows an exemplary aspect of the present invention pertaining tohow uplink and downlink frequencies can be inverted;

FIG. 19 shows the interference paths between the satellite, basestation, and user terminals;

FIG. 20 shows the user of a base station antenna having a null in thegeostationary arc;

FIG. 21 shows an exemplary method of call initialization;

FIG. 22 shows the use of transition channels;

FIG. 23 shows an exemplary method of satellite to base-stationproximity-initiated hand-off; and

FIG. 24 shows an exemplary method of base station-to-satellite and basestation-to-base station proximity-initiated hand-off.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and to the arrangements of the componentsset forth in the following description or illustrated in the drawings.The invention is capable of other embodiments and of being practiced andcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein are for the purpose ofdescription and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception,upon which this disclosure is based, may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the invention be regarded as including equivalentconstructions to those described herein insofar as they do not departfrom the spirit and scope of the present invention.

FIG. 5 shows an exemplary high level block diagram of a standard system500 that can be used to implement the frequency assignment, reuse and/orreassignment, and other features of the present invention. Thetelemetry, tracking and command (TT&C) facility 502 is used to controland monitor the one or more satellites 516 of the system 500.

The terrestrial segment can optionally use, for example, digitalcellular technology, consisting of one or more Gateway Station Systems(GSS) 504, a Network Operations Center (NOC) 506, one or more MobileSwitching Centers (MSC) 508, one or more Base Transceiver Stations (BTS)514, and a variety of mobile, portable, and/or fixed subscriberterminals 512. The subscriber terminals 512 can be equipped with aSubscriber Identity Module (SIM) (not shown) or similar module thatidentifies the individual subscriber terminal 512. The subscriberterminals 512 are generally handheld devices that provide voice and/ordata communication capability. Subscriber terminals 512 may also haveadditional capabilities and functionality such as, for example, paging.Equipping the subscriber terminals 512 with a SIM module can allow theuser to have access to the system 500 by using any subscriber terminals512 having a SIM.

The MSC 508 preferably performs the switching functions of the system500, and also optionally provides connection to other networks (e.g.,Public Data Network (PDN) 516, and/or Public Switched Telephone Network(PSTN) 518). BTSs 514 can be used in those areas where the satellitesignal is attenuated by, for example, terrain and/or morphologicalfeatures, and/or to provide in-building coverage. The BTSs 514 and BSCs510 generally provide and control the air interface to the mobileterminals 512. It is preferred that the BTSs 514 use a wirelessproprietary or standard wireless protocol that is very similar to thatof the satellites 516. The BSC 510 generally controls one or more BTSs514 and manages their radio resources. BSC 510 is principally in chargeof handovers, frequency hopping, exchange functions and control of theradio frequency power levels of the BTSs 514.

NOC 506 can provide functions such as monitoring of system power levelsto ensure that transmission levels remain within tolerances, and linemonitoring to ensure the continuity of the transmission lines thatinterconnect the BSC 510 to the BTS 514, the MSC 508 to the PDN 516 andthe PSTN 518, and the NOC 506 to other network components. The NOC 506can also monitor the satellite 516 transponders to ensure that they aremaintained within frequency assignment and power allocation tolerances.The NOC also optionally performs priority and preemption to ensure thatcommunication resources are available and/or assigned, reused and/orborrowed in a timely manner to, for example, facilitate callsoriginating and/or transmitted to a subscriber terminal 512. Toeffectuate the dynamic channel assignment and priority and preemptionfeatures of the present invention, the NOC generally maintainscognizance of the availability of satellite and/or terrestrial resourcesand arranges for any necessary satellite reconfiguration and/orassignment and or reuse of frequencies to meet changed traffic patterns.U.S. Pat. Nos. 5,926,745, 5,815,809, 6,112,085, and 6,058,307 areincorporated herein by reference.

The system 500 will also have one or more satellites 516 thatcommunicate with the satellite GSS 504 and the subscriber terminals 512.A typical GSS 504 will have an antenna to access the satellite. On theuplink transmission path, the GSS 504 will generally have upconvertersthat can translate the GSS 504 IF frequency to the feeder linkfrequency. On the downlink transmission path, the received signal ispreferably amplified, and feeder link frequencies are translated to thecommon IF frequency.

FIG. 6 is an exemplary BTS 514 frequency plan. The nomenclature isprovided as follows:

-   -   f^(U) _(1a) and f^(D) _(1a)    -   superscripts U and D indicate uplink and downlink, respectively;    -   the numeric subscript (e.g., 1) indicates the frequency band;        and    -   the letter subscript (e.g., a) indicates the frequency channel        within the frequency band.

The satellite frequency band generally comprises uplink and downlinkfrequencies, each of which in turn generally comprise a range ofseparated frequencies (e.g., 1626.5-1660.5 MHz for uplink, and 1525-1559MHz for downlink). The present invention is not limited, however, tosharing frequencies within a single frequency band assigned and/ordesignated by, for example, a government regulatory agency. The presentsystem may also therefore, share and/or reuse frequencies of otherdomestic, foreign, and/or international satellite and/or terrestrialsystems, subject to, for example, national, foreign, and/orinternational government regulatory approval. In addition, as defined inconnection with the present invention, a frequency comprises any set offrequencies that have been associated with a particular frequency band,and is not limited to a consecutive set or series of frequencies withina band. Further, a frequency band in alternative embodiments maycomprise a logical set of frequencies that may be assigned to differentcommunication systems, carriers, or in other predesignated frequencybands. That is, for example, a frequency band in the present inventionmay include frequencies that are assigned to other frequency bands, forexample, for different purposes.

Conventionally, users communicating on uplink 604 and downlink 602 woulduse, for example, paired uplink and downlink channels f^(U) _(1a) andf^(D) _(1a), f^(U) _(2a) and f^(D) _(2a), f^(U) _(3a) and f^(D) _(3a),etc. Advantageously, in the present invention, different channels withinthe same frequency band are optionally assigned, reused and/orreassigned in a non-pairwise manner. For example, downlink 602 could beusing f^(D) _(1a), whereas uplink 604 could be using f^(U) _(1b).Similarly, downlink 602 could be using f^(D) _(1c) whereas uplink 604could be using f^(U) _(1d). These pairings are illustrative only,insofar as numerous other non-pairwise uplink 604 and downlink 602combinations are available that can be used, for example, withindifferent terrestrial cells within subareas, within different subareasof a spot beam, and/or between different spot beams.

Further, suppose that f^(U) _(2a) and f^(D) _(2a) are the uplink anddownlink frequency bands associated with a second domestic or foreignsatellite system. Users of system 500 communicating on downlink 602 anduplink 604 could use, for example, uplink and downlink frequencies f^(U)_(1a) and f^(D) _(2a), f^(U) _(1c) and f^(D) _(2b), f^(U) _(1b) andf^(D) _(2c), etc. In general, the present invention optionally uses oneor more uplink and downlink channels that are from different frequencybands and/or associated with a different domestic and/or foreignsatellite system.

FIG. 7 is an exemplary high level block diagram of a GSM system that canuse the frequency reuse schemes in accordance with the presentinvention. As previously noted, the present invention is not limited touse with a GSM system, and can be deployed with all satellite (e.g.,LEO, MEO, GEO, etc.) and cellular terrestrial technologies (e.g., TDMA,CDMA, GSM, etc.).

An exemplary Home Location Register (HLR) 706 comprises a database thatstores information pertaining to the subscribers belonging to thecoverage area of a MSC 508. The HLR 706 also stores the current locationof these subscribers and the services to which they have access. In anexemplary embodiment, the location of the subscriber corresponds to theSS7 704 address of the Visitor Location Register (VLR) 702 associated tothe subscriber terminal 512.

An exemplary VLR 702 contains information from a subscriber's HLR 706 inorder to provide the subscribed services to visiting users. When asubscriber enters the covering area of a new MSC 508, the VLR 702associated with this MSC 508 will request information about the newsubscriber to its corresponding HLR 706. The VLR 702 will then haveenough information in order to ensure the subscribed services withoutneeding to ask the HLR 706 each time a communication is established. TheVLR 702 is optionally implemented together with a MSC 508, so the areaunder control of the MSC 508 is also the area under control of the VLR702.

The Authentication Center (AUC) 708 register is used for securitypurposes, and generally provides the parameters needed forauthentication and encryption functions. These parameters help to veritythe user's identity. Terrestrial cells 816 can also be positioned sothat they cover at least a portion of two or more spot beams (e.g., 802,804) and/or two or more subareas (e.g., 820, 822)

FIG. 8 a shows a first exemplary embodiment of a frequency sharingand/or reuse scheme in accordance with the present invention. Generally,the capacity of a satellite network utilizing spot beams is directlyproportional to the number of times a cluster of spot beams isreplicated. Although FIG. 8 a shows a cluster size N of seven (7) (i.e.,seven spot beams) (802, 804, 806, 808, 810, 812, 814), the presentinvention can equally be practiced with other cluster sizes or numbers.FIG. 8 a does not show the terrestrial system underlaying each of therespective spot beams (802-812), each of which will typically include atleast one terrestrial cell 816.

The FIG. 8 a embodiment advantageously enhances spectrum usage byallocating at least a portion of the spectrum of, for example, at leasta first satellite spot beam (e.g., 802-812) to an underlay terrestrialsystem associated with or having overlapping coverage with, for example,at least a second satellite spot beam (e.g., 814), while minimizinginterference between each of the respective satellite and terrestrialsystems that reuse and/or share a portion of the spectrum. The presentinvention may optionally apply to any combination of systems havingoverlapping coverage, including terrestrial-terrestrial systems and/orsatellite-satellite systems.

With regard to spot beams 802-814, a superscript T represents aterrestrial system, and the frequencies without a superscript Trepresent satellite systems. As shown, the terrestrial frequency sets(designated by (f₃, f₂, f₄, f₁, f₅)^(T), etc.) associated with the spotbeam 814 use, are assigned, or reuse in various combinations, f₁, f₂,f₃, f₄, f₅, and/or f₆. For purposes of explaining at least one aspect ofthe present invention, it is assumed that each spot beam has a frequencyset containing nine (9) 200 kHz channels f₁={q_(i,1), q_(i,2), q_(i,3),. . . , q_(i,9)} for i=1 . . . 7), as discussed with reference to FIG.5. Other quantities of channels and/or associated bandwidths thereof mayoptionally be used. It is also assumed that there is a spot beam toadjacent spot beam average isolation of, for example, 10 dB, althoughthe present invention is also compatible with, or applies to, differentspot beam isolations.

In this configuration, each spot beam (802-814) is assigned a set offrequencies that will be used exclusively by, or substantially used byor assigned to, the satellite network f_(i). Likewise, the terrestrialnetwork in each spot beam uses a set of frequencies exclusive to, orsubstantially used by or assigned to, the terrestrial network ( f_(i))^(T). For example, the satellite frequencies used in the centerspot beam 814 is f₇, and the terrestrial frequencies in this spot beamcan include all other frequency sets {f₁, f₂, f₃, . . . , f₆}=( f₇)^(T). That is, the channels used by center spot beam 814 arepreferably not used by the underlay terrestrial system associated withthe spot beam 814. In this manner, the different channels are preferablyallocated among the various spot beams (802-814) and associated underlayterrestrial systems such that any interference between them isminimized. Note that in this configuration the entire spectralallocation is shared or substantially shared between the satellitenetwork and the terrestrial network in each of the seven spot beams802-814, although other sharing or overlapping coverages are optionallyused. Further, while center spot beam 814 has been designated in thisembodiment, other spot beams that are not directly center to the spotbeam/terrestrial coverage may be selected alternatively.

Spot beam 814 generally comprises two areas. The first is an area 818generally central to spot beam 814, where channels from any or all ofspot beams adjacent to spot beam 814 (i.e., spot beams 802, 804, 806,808, 810 and/or 812) can be assigned, borrowed, and/or reusedterrestrially. The second area comprises subareas 820, 822, 824, 826,828, and 830. As shown in FIG. 8 a, in areas 820-830, all frequenciescan be assigned, borrowed, and/or reused terrestrially, but preferablynot those frequencies used in an adjacent spot beam. For example, insubarea 822, channels associated with spot beams 810, 808, 812, 806, and802 can be reused terrestrially. However, as previously noted, channelsassociated with spot beam 804 are preferably not used in subarea 822, orany terrestrial cells within subarea 822.

If, as previously assumed, each spot beam 802-814 has, for example, nine(200 kHz) channels associated therewith, there would be sixty threechannels that could potentially be assigned, reallocated and/or reusedbetween the satellite and/or the respective underlay terrestrialsystems. The satellite 516 may use, for example, nine (9) of thechannels per spot beam of the 7 cell reuse pattern, and the remainingfifty four (54) channels could therefore be allocated to the respectiveunderlay terrestrial systems associated with the spot beams (802-814).Therefore, each spot beam subarea (820-830), excluding central area 818,will have 45 terrestrial channels available. Other division of channelsmay also be used.

For example, consider subarea 820. Since each of f₂, f₃, f₄, f₅ and f₆has 9 channels, 45 terrestrial channels are thus available in subarea820. Similarly, 45 channels are also available within subareas 822-830.It should be understood that this example is illustrative, and notlimiting, insofar as the present invention generally works regardless ofhow many spot beams there are or how many channels there are persatellite coverage area and/or terrestrial coverage area.

Careful frequency planning can help to reduce interference throughmaximizing satellite-terrestrial frequency reuse distance. Todemonstrate this concept, again consider a terrestrial network in thecenter spot beam in FIG. 8 a. Suppose again that the terrestrial networkhas 45 available RF channels for reuse. Any satellite frequency setsthat do not include channels associated with spot beam 814 can be usedin the terrestrial network to provide adjacent beam isolation.

However, a random selection from the pool of 54 frequencies availablefor terrestrial use may result in areas where the distance between theterrestrial frequencies and satellite frequencies used in the adjacentspot beams is not substantially maximized. Selective assignment ofterrestrial frequencies to the immediate area adjacent to each spot beamin accordance with the present invention can result in increasedsatellite-terrestrial channel reuse distance.

FIG. 8 a shows an exemplary terrestrial frequency allocation thatresults in increased and possible substantially maximumterrestrial-satellite frequency distance. As shown, in each subarea(820, 822, 824, 826, 828, 830), the terrestrial frequency sets have beenselected in order to maximize the frequency reuse distance from thesatellite frequency sets in adjacent spot beams.

For example, with regard to subarea 820, spot beam 808, having assignedfrequency set f₄, is the farthest away. The spot beams with next largestdistance are 810 and 806, having the assigned satellite frequency setsf₃, and f₅, respectively. Finally, spot beams 802 and 804 have theassigned frequency sets f₂ and f₆, respectively. In general, theterrestrial network within each spot beam is preferably sectioned in thesame way that has been done for spot beam 814.

With regard to frequency channels associated with spot beams 812 and 808(and spot beams 802 and 806), frequency channels from spot beam 812 and808 can be reused in subarea 822 in either order, or even randomly,since they are each substantially equidistant from subarea 822.Similarly, frequency channels from spot beams 812 and 808 can be usedalternately (e.g., reusing a channel from spot beam 808, reusing a spotbeam from channel 812, and repeating), or even randomly. The order inwhich frequency channels can be reused and/or reassigned, therefore, isvirtually infinite.

Spot beams 802-814 can be positioned to cover predetermined areas. Oneor more spot beams 802-814 can also be dynamicallyconfigured/reconfigured to cover an area based on, for example, currentand/or anticipated loading considerations.

As will be discussed with regard to FIGS. 14 a and 14 b, increasingterrestrial cluster size within a satellite spot beam can also beutilized to decrease co-channel interference.

In general, it is therefore preferred that the separation between theterrestrial channels and the satellite channels be maximized which, inturn, generally, tends to minimize the interference between adjacentspot beams (e.g., 802 and 804) and adjacent subareas (e.g., 820 and822). However, even when these objectives are accomplished, thetransmissions by the terrestrial network(s) will generally, to a certainextent and depending on the local attenuation, be “heard” by theassociated satellite. Therefore, as shown in FIG. 8 a, frequency reuseplanning must be carefully done preferably along adjacent spot beamboundaries (e.g., 802 and 804) to ensure that interferences areminimized.

As described above, the present invention generally utilizes theinter-spot beam isolation (e.g., the isolation between the various spotbeams), to reduce interference. In other words, an exemplary embodimentof the present invention takes the co-channel, co-beam and “transfers”it to co-channel, adjacent beam interference.

Within each spot beam (e.g., 802-814), the use of satellite frequenciesby the terrestrial network results in co-channel/adjacent-beaminterference. To utilize the isolation rendered by the availability ofthe spot beams, satellite terrestrial frequency reuse should preferablybe implemented on adjacent spot beams. The resulting co-channel/adjacentbeam interference will generally be approximately reduced by the spotbeam to adjacent spot beam isolation factor. It should be noted,however, that in a cluster of, for example, seven spot beams, as shownin FIG. 8 a, each spot beam 802-812 has six adjacent spot beams that cancontribute to the interference received. The advantage ofco-channel/adjacent beam technique over co-channel/co-beam technique laywith the fact that not all spot beams have equal service demand.Consequently, the distribution of interference between adjacent spotbeams can reduce the average interference in a high service demand beam.Any energy that is being generated by the spot beam channels within a814 spot beam (e.g., 814) can be attenuated by the antenna pattern ofthe spot beam 814 satellite.

The frequency reuse scheme in accordance with the present inventiontherefore enables the total frequency band to be efficiently allocated(e.g., based on demand) between the terrestrial and satellite systemswithin each of the seven spot beams (802-814) and each of the respectiveterrestrial underlay systems associated therewith, while minimizinginterference therebetween.

Consider FIG. 8 a from a geographic perspective. As shown, New York cityfalls within spot beam 802, as well as terrestrial cell 816,Philadelphia falls within spot beam 814 and subarea 826, and Washington,D.C. falls within spot beam 808. Although terrestrial cells 816 can belocated anywhere within the satellite spot beams (802-814), they willgenerally be located in, for example, metropolitan areas (e.g., NewYork, N.Y.) where satellite coverage may be limited due to, for example,capacity constraints or no line of sight or reduced line of sightbetween a subscriber terminal 512 and a satellite 516. This is oneillustrative configuration, and is not intended to limit the inventionin any way. If desired, spot beams 802-814, subareas 820-830, and/orterrestrial cells 816 can optionally be increased, decreased, and/orvaried in number, size, and/or arrangement to yield a virtually infinitenumber of configurations that may be tailored to suit one or moregeographic areas.

In general, the channels associated with one particular spot beam orarea of coverage can be reassigned for satellite and/or terrestrialreuse in conjunction with any other spot beam or area of coverage. Ifone spot beam (e.g., 814) gets too congested, it can borrow and/or reusefrequency spectrum from other spot beams (e.g., 802, 804, 806, 808, 810and/or 812) that have available capacity. The frequencies being assignedare thus preferably location dependent upon, for example, the locationof the spot beam. Thus, if spot beam 802 has nine frequencies and onlythree of the nine frequencies are needed for satellite transmission, theremaining six frequencies can dynamically be reassigned to eitheranother system, such as a terrestrial system or other satellite system,or to increase capacity in, for example, an adjacent (i.e., 804, 812,and/or 814) or non-adjacent (i.e., 806, 808, and/or 810) satellite spotbeam.

At some point, the spot beam 808 channels that are reused terrestriallywithin spot beam 814 will interfere with the spot beam 808 satellitetransmissions. However, any potential interference can be minimized bymanaging the frequency reuse and the size of these networks.

As discussed above, it is preferred that those frequencies associatedwith a spot beam furthest away be reused first, and that thosefrequencies associated with a spot beam closest (i.e., adjacent) to thespot beam which will reuse the frequency be used last. Again referringto subarea 822 and/or any terrestrial cells having at least partiallyoverlapping coverage therewith, it is therefore preferred that channelsfrom spot beam 810 be reused first, then channels from spot beams 808and 812 be reused, and then channels from spot beams 802 and 806 bereused. An alternative or in addition, frequencies may be reassignedresponsive to the congestion load in adjacent or nearby cells such thatsubstantially equidistant cells are selected based on lower congestionor capacity rate, and even cells that are closer may alternatively beselected over cells that are further away based on congestion, loadand/or capacity constraints.

In highly populated areas where terrestrial coverage can present greatspectral efficiency over the satellite coverage, the terrestrial cellsite density will be high. Accordingly, the interference generated inthese cell sites will also be high. In such circumstances, it isadvantageous to trade part of the satellite frequency spectrum of thespot beam (and even part of adjacent spot beams) to the terrestrialnetwork. Such a trade off results in lower co-channel interferencelevels. As an example of a frequency borrowing technique, consider theexample discussed in the previous section where each of the terrestrialnetworks have been configured with 45 RF channels and the satellitenetwork in the corresponding spot beam has been configured with nine (9)RF channels. To reduce the interference by increasing the cluster size,three (3) channels from the satellite network can be reassigned to theterrestrial network resulting in 48 channels for reuse terrestrially andsix (6) channels for the corresponding satellite spot beam.

The channels within spot beam 808, for example, can also be used as aterrestrial frequency in, for example, spot beam 814. It is preferredthat the channels in spot beam 808 are used in five of the six subareas,and/or respective terrestrial cells associated therewith, of spot beam814 (i.e., subareas 820, 822, 824, 828 and 830). As shown in FIG. 8 a,it is also preferred that the channels of spot beam 808 not be used insubarea 826 (i.e., in the subarea that is contiguous with and directlyadjacent to the spot beam 808). However, in alternate embodiments,depending on load and/or capacity issues, directly adjacent cells mayalso be utilized for frequency assignment and/or reuse.

FIG. 8 b shows a first exemplary embodiment of frequency reuse in aseven cell pattern. As discussed with regard to FIG. 8 a, thefrequencies assigned, borrowed and/or reused are preferably taken fromthe spot beam furthest away from the assigned, reusing, or borrowingsubarea and/or terrestrial cell(s) associated therewith.

FIG. 8 c shows a variation of the first exemplary embodiment shown inFIG. 8 a. In FIG. 8 c, spot beams 803, 805, 807, 809, 811, 813, and 815are depicted as being circular, and respectively correspond to spotbeams 802, 804, 806, 808, 810, 812, and 814 shown in FIG. 8 a.Similarly, subareas 850, 852, 854, 856, 858, and 860 respectivelycorrespond to subareas 820, 822, 824, 826, 828, and 830 shown in FIG. 8a. In FIG. 8 c, subareas 850-860 have a different shape than subareas820-830 shown in FIG. 8 a, and generally extend from the center portion818 to the dashed line of the respective adjacent subcell that partiallyoverlaps with the area of coverage of spot beam 815. Aspects of thepresent invention discussed in connection with FIG. 8 a pertaining tofrequency borrowing, assignment and reuse are also generally applicableto FIG. 8 c.

FIG. 9. shows an exemplary method by which the size of satellite spotbeams (802-814) can be determined. Specifically, as shown in FIG. 9,cell size (e.g., cell diameter) can be determined as being approximateto the distance corresponding to a 3 dB loss. That is, an exemplaryradius of a satellite spot beam (802-814) in accordance with the presentinvention is preferably determined as being approximately equal to thedistance over which maximum signal strength decreases by approximately50%. Therefore, assuming that satellite 516 can generate, for example,seven spot beams having substantially equal power, the radius of eachspot beam (802-814) is determined from a point of maximum gain to thepoints having approximately a 3 dB loss. Other signal strength decreasepercentages and/or techniques for determining the size and shape of thesatellite cells, and/or center areas may optionally be used.

FIG. 10 shows an exemplary method by which a substantially central area818 is determined. Specifically, in accordance with the presentinvention, we have determined that channels from all adjacent spot beams(802-814) can be reused in an area 818 that is equal to approximately25% of the area of spot beam 814. Insofar as an infinite number of linesegments, each having a different distance and radius, can be drawn fromcenter 819 of spot beam 814 to one of its adjacent sides (e.g., segment850, 854), there can be an infinite number of substantially equal areaswithin a spot beam (802-812) where channels from all adjacent spot beamscan be reused. In accordance with one embodiment, we have determinedthat the maximum radius will correspond to a radius extending from thecenter or substantially the center of spot beam 814 (at 819) to point850 (or 854), and a minimum area will correspond to a radius extendingfrom the center of spot beam 815 (at 819) to point 852, which bisectssegment 850, 854. Other methods of determining the size and/or shape ofarea 818 may also be used, and area 818 may be of any shape including,for example, rectangular, hexagonal, and the like.

FIG. 11 a shows a second exemplary embodiment of frequency reuse withina satellite spot beam. Although FIG. 11 a differs from FIG. 8 a in thatFIG. 11 a does not have a central area 818 as shown in FIG. 8 a,terrestrial cells along the interior boundaries of spot beam 814 maynevertheless utilize all frequencies (f₁-f₆) . Other aspects of theinvention pertaining to, for example, frequency assignment, reuse and/orborrowing discussed in connection with the FIG. 8 a embodiment aregenerally applicable to the embodiment shown in FIG. 11 a. That is, theembodiment shown in FIG. 11 a advantageously enhances spectrum usage byallocating at least a portion of the spectrum of, for example, at leasta first satellite spot beam (e.g., 1102-1112) to an underlay terrestrialsystem preferably associated with or having overlapping coverage with,for example, at least a second satellite spot beam (e.g., 1114), whileminimizing interference between each of the respective satellite andterrestrial systems that reuse and/or share a portion of the spectrum.FIG. 11 a may also optionally apply to any combination of systems havingoverlapping coverage, including terrestrial-terrestrial systems and/orsatellite-satellite systems. In addition, frequencies may be reassignedresponsive to the congestion load in adjacent or nearby spot beams,subareas, and/or terrestrial cells such that, for example, substantiallyequidistant spot beams and/or subareas are selected based on lowercongestion or capacity rate, and even subareas that are closer mayalternatively be selected over subareas that are further away based oncongestion, load and/or capacity constraints.

FIG. 11 b shows a variation of the second exemplary embodiment shown inFIG. 11 a. Spot beams 1103, 1105, 1107, 1109, 1111, 1113, and 1115 aredepicted as being circular, and respectively correspond to spot beams1102, 1104, 1106, 1108, 1110, 1112, and 1114 shown in FIG. 11 a.Similarly, subareas 1150, 1152, 1154, 1156, 1158, and 1160 respectivelycorrespond to subareas 1120, 1122, 1124, 1126, 1128, and 1130 shown inFIG. 11 a. In FIG. 11 b, subareas 1150-1160 have a different shape thansubareas 1120-1130 shown in FIG. 11 a. In FIG. 11 b, subareas generallyextend from the center or substantially the center of spot beam 1115 tothe dashed line of the respective adjacent subcell having partiallyoverlapping coverage with spot beam 1115.

Further, in areas where spot beams overlap (e.g., 1170, 1172, 1174,1176, 1178, and 1180), there may be increased interference due to theoverlapping coverage of the respective spot beams. In subareas1150-1160, all frequencies associated with adjacent spot beams 1103-1113could be used. This could depend, for example, on the need for spectrumterrestrially and frequency separation distance. For example, in subarea1150, although frequencies f₄, f₃, f₅, f₂ and f₆ are first preferablyborrowed, assigned and/or reused terrestrially, f1 may also be borrowed,assigned and/or reused terrestrially. If any of the f₁ frequencies areborrowed, assigned or reused terrestrially in subarea 1150, it ispreferred that, in order to reduce interference, they be borrowed,assigned or reused in one or more terrestrial cells near the center ofspot beam 1115. However, the f₁ frequencies can also be used in aterrestrial cell 1132 near area 1170 but within subcell 1152. Otheraspects of the present invention discussed in connection with FIG. 11 apertaining to frequency borrowing, assignment and reuse are alsogenerally applicable to FIG. 11 b.

As shown in FIG. 12, satellite spot beams at the edge of the servicearea (1202, 1204, 1206, 1208, 1210) do not have the full complement ofsix neighbors. As such, the terrestrial network within the areas coveredby this type of spot beams will have slightly different configuration.FIG. 12 shows an exemplary terrestrial network frequency plan for such aspot beam.

Spot beam 1210, having assigned frequency channels f₇, has only threeadjacent spot beams 1202, 1204, 1206. Spot beams with frequency channelsf₂, f₃, and f₄ are missing from the cluster. As a result, the f₂, f₃,and f₄ frequency channels can be assigned to all subareas (1212, 1214,1216, 1218, 1220, 1222) of spot beam 1210. The remaining terrestrialfrequency assignments for subareas 1212-1222 follow the proceduredescribed above with regard to FIG. 8 a, with the exception of subarea1220. In subarea 1220, there are two choices for one frequency channelassignment, f₅ and f₁, either of which can be assigned to subarea 1220.This is because both f₁, and f₅ are equidistant from subarea 1220.Accordingly, assignment of frequencies can be based on load and/orcapacity issues in the spot beams with frequencies f₁ and f₅, as well asother methods of determining which of the spot beams with frequencies f₁and f₅ are preferred.

FIG. 13 is an exemplary flowchart illustrating a process of assigningand/or reusing frequencies. In step 1302, spot beams are divided into anumber of subareas. Different sized and/or different shaped cells mayalternatively be used. In accordance with one embodiment of the presentinvention, the spot beam may also have an optional central portion 818as shown in FIG. 8 a. A determination is then made at step 1304 as towhether underlay terrestrial frequencies are required in the spot beam.If not, the process ends at step 1306.

If terrestrial frequencies are required, then a determination is made atstep 1308 as to whether frequencies are required in a central portion ofthe spot beam. If yes, then frequencies of other spot beams can be usedin the central portion of the spot beam at step 1310, whereafter themethod proceeds to decision step 1312. If frequencies are not requiredin a central portion of the spot beam, then at decision step 1312 adetermination is made as to whether terrestrial frequencies are requiredin any of the subareas. If yes, then at step 1314 frequencies are reusedfrom the most distant spot beams relative to each required subarea (aspreviously discussed with regard to and indicated in FIG. 8 a). Atdecision step 1316, a determination is made whether additionalfrequencies are required. If so, the process returns to decision step1308. If not, the process ends at step 1306.

FIG. 14 is an exemplary flowchart illustrating a method by whichfrequencies can be assigned when they are equidistant from a cell orsubarea to which they are assigned. At decision step 1402, adetermination is made whether the cell or coverage area to which thefrequencies are to be assigned, reused and/or shared is substantiallyequidistant from the cell or coverage area from which they are taken. Ifnot, the frequencies associated with a cell or coverage area furthestaway from the coverage area to which the frequencies are to be assigned,reused and/or shared are preferably used, as discussed with regard toFIG. 13. the process then ends at step 1406.

If the cell or coverage area to which the frequencies are to beassigned, reused and/or shared is substantially equidistant from thecell or coverage area from which they are taken, at decision step 1408 atime interval for which the frequencies can be borrowed can optionallybe utilized. If a time interval is selected at decision step 1408, thetime interval may consider, for example, historical usage patterns whenevaluating excess capacity of equidistant cells at step 1412. Forexample, with regard to FIG. 12, spot beams 1202 and 1208 areequidistant from subarea 1220. If, for the time period underconsideration, spot beam 1208 has a historically higher usage than spotbeam 1202, frequencies can first be borrowed from spot beam 1202. Otherfactors such as signal to interference ratio, and signal strength canalso be used in determining the order in which frequencies are assigned,reused and/or shared. If a time interval is not used, then, at step1412, the assignment, reuse and/or sharing determination is preferablybased on, for example, current loading considerations. As discussed withregard to step 1412, other factors such as signal to interference ratio,and signal strength can also be used in determining the order in whichfrequencies are assigned, reused and/or shared. At step 1414,frequencies are assigned, reused or borrowed such that the probabilitythat each cell from which frequencies are taken has substantially thesame probability that frequencies will not be exhausted therein. When atime interval is selected at step 1410, step 1414 will generally takeinto consideration historical usage, as discussed above. When a timeinterval is not chosen, probabilities will generally be evaluated basedupon, for example, current usage.

FIG. 15 is an exemplary flowchart illustrating a method by whichfrequencies can be dynamically assigned. At step 1502, frequency usageis monitored within each spot beam and/or subarea. When, as determinedat decision step 1504 that there are incoming calls, a determination ismade at decision step 1506 whether sufficient channels are available. Ifso, then frequencies are allocated in accordance with existing channelassignments. If sufficient channels are not available, then, at step1510, frequencies are assigned, reused and/or shared to providesufficient bandwidth. As discussed with regard to FIG. 14, one criteriaby which frequencies can be assigned, reused and/or shared can be basedon substantially equalizing the probability that each cell from whichfrequencies are borrowed frequencies will not be exhausted. As indicatedat decision step 1512, channels can again be reassigned if, for example,interference levels are not acceptable. At step 1514, calls areallocated to channels in accordance with updated channel assignments,after which the process either returns to step 1502 or terminates, asdetermined at decision step 1516.

FIG. 16 is an exemplary flowchart illustrating a method by whichfrequencies can be preemptively reassigned based on, for example, loadbalancing and/or capacity issues. At step 1602, frequency usage ismonitored within each spot beam and/or subarea. When, as determined atdecision step 1604 that there are incoming calls, a determination ismade at decision step 1606 whether sufficient channels are available. Ifso, then at step 1608 frequencies are allocated in accordance withexisting channel assignments. If sufficient channels are not available,then, at step 1610, a time interval is selected. At step 1612, and basedupon the time interval selected at step 1610, frequencies are assigned,reused and/or shared to provide sufficient bandwidth. As discussed withregard to FIG. 14, one criteria by which frequencies can be assigned,reused and/or shared, based on a selected time interval, can be that ofsubstantially equalizing the probability that each cell from whichfrequencies are borrowed frequencies will not be exhausted. This, inturn, can be based, for example, on historical usage patterns for theaffected area(s) and/or selected time interval. As indicated at decisionstep 1614, channels can again be reassigned at step 1612 if, forexample, interference levels are not acceptable. At step 1616, calls areallocated to channels in accordance with updated channel assignments,after which the process either returns to step 1602 or terminates, asdetermined at decision step 1618.

As shown in FIGS. 17 a and 17 b, one technique and alternativeembodiment that may be practiced with the present invention isincreasing the cluster size. This will generally minimize theinterference between the satellite and terrestrial systems.

FIG. 17 a shows a traditional GSM type of pattern of four cells withthree sectors each. If instead, as shown in FIG. 17 b, twenty-fourchannels are assigned across the cells, then one site in eight has thesame frequency, as opposed to one site in four having the same frequencyas with the traditional GSM pattern of FIG. 17 a. Thus, the number ofinstances where the same frequency exists has been halved, and theamount of energy on an individual channel has also been reduced byapproximately half. In this example, the interference between thesatellite and terrestrial systems would be reduced by approximately 3 dBvis-à-vis the traditional GSM system.

Cross network interference occurs when a channel is utilized both in theterrestrial network and in the satellite network, either in the co-beamconfiguration or in the adjacent-beam configuration. The severity ofsuch interference depends on the power received by the competingnetwork. In particular, the terrestrial networks use or reuse an RFchannel or channels many times in an area covered by a given satellitespot beam or beams. Each occurrence of this channel gives rise toincreased co-channel interference for the satellite network.

In the case of the co-beam configuration, the co-channel interferencecan be approximated by MI, where M is the number of times a channel isreused and I is the interference power of one source. For theadjacent-beam configuration the co-channel interference from oneadjacent beam can be approximated by αMI, where a accounts for thefraction of power leaked from the adjacent beam. Thus, in both co-beamand adjacent beam configuration, the co-channel interference is directlyproportional to the number of times a particular frequency is reusedterrestrially.

Again with regard to FIGS. 17 a and 17 b, by increasing the cluster sizefor the terrestrial network, the reuse of a particular frequency isreduced. To illustrate the point, consider a terrestrial network asshown in FIG. 17 a that has 12 available RF channels for reuse with acluster size of four and three sectors per cell site. In eachterrestrial cluster, the skyward energy from one sector will or mayinterfere with all satellite co-channels in the adjacent spot beams (inthe same spot beam for co-beam configuration). FIG. 17 b shows aterrestrial network with 16 cell sites (48 sectors), each RF channel isrepeated four times in this network. In this same 16 site network, iftwenty-four RF channels are used, for example, in a cluster of 8, thenthe number of co-channel sectors is reduced from 4 to 2. In general,this type of tradeoff between bandwidth and interference can be employedwith the present invention to reduce co-channel interference.

The frequency inversion technique, as shown in FIGS. 18 a and 18 b,involves reversing the satellite down-link (F₁) and satellite up-link(F₂) frequencies to become the terrestrial up-link (“return-link”) andterrestrial down-link (“forward-link”) frequencies, respectively. As aresult, there will be two possible interference paths, as shown in FIG.19: (1) between the satellite 516 and base stations 1802, as return-linkto down-link interference on F₁, and as up-link to forward-linkinterference on F₂; and (2) between the satellite user terminals 1804and terrestrial user terminals 1806, as down-link to return-linkinterference on F₁, and as forward-link to up-link interference on F₂.The system and method according to the present invention eliminates orsubstantially reduces both of these possible interferences, as will bedescribed herein. It should be understood that the system may compriseone or more base station antennas (and associated base stations) and oneor more satellites, although only one of each are shown in FIG. 19. Itshould also be understood that the system may comprise one or moresatellite handsets and one or more base station handsets, although onlyone of each are shown in FIG. 19.

As shown in FIG. 20, interference between the satellite 516 and basestations 1802 (i.e., return-link to down-link and up-link toforward-link interference) is substantially reduced or eliminated,preferably by using a base station antenna having a substantiallyreduced gain in the geostationary arc (i.e., the elevation angle abovethe horizon from a base station to the satellite). Unlike a userterminal 1804, 1806, which is mobile and may be oriented differentlyfrom user to user, a base station 1802 does not move and therefore formsa substantially fixed angular relationship with respect to thesatellite. Within North America, the geostationary arc typically variesfrom approximately 30° to 70°, depending, for example, on the latitudeof the base station. To fully take advantage of this fact, it ispreferred that the base station antenna pattern have a null, andtherefore significantly reduced gain, in the geostationary arc portionof its vertical pattern. As an analogy, one could consider the satelliteto be in a “blind spot” with respect to the base station. The additionalsignal attenuation achieved from this technique substantially reduces oreliminates interference between the satellite and terrestrial basestations. This technique will facilitate terrestrial coverage and at thesame time substantially reduce or eliminate interference to thesatellite system.

To further enhance the performance of the system, a technique foroptimally or substantially optimally locating and orienting basestations will preferably be used, to advantageously utilize thehorizontal gain pattern of the antenna. The benefits of using thistechnique, for example, are that frequency reuse will be maximized orsubstantially maximized, thereby enhancing the overall capacity of thesystem, and further reducing or eliminating interference.

In addition to the increased isolation provided by the vertical antennapattern, additional isolation can be obtained from the horizontalantenna pattern. For example, preferably by configuring base stationssuch that the azimuth to the satellite is off-bore or between sectors,several additional dB of isolation can typically be achieved. By keepingthis configuration standard for, say, a cluster of base stations,frequency reuse for the terrestrial system can generally be increased.

Interference between satellite user terminals 1804 and terrestrial userterminals 1806 is typically a problem when the units are in relativelyclose proximity to one another. It is preferred that such interferencebe substantially reduced or eliminated by, for example, first detectingclose proximity before the assignment of a radio channel (i.e., duringcall initialization), and secondly by providing a hand-off to anon-interfering channel if close proximity occurs after the assignmentof a radio channel. The call initialization method shown in FIG. 21allows for real-time or near real-time operation of this technique.

The technique provides optimum or substantially optimum radio resourceallocation so that the coexistence of single-mode terminals (satellitemode) and dual-mode terminals can be accomplished. In order for this towork, it is preferred that a relatively small group of channels, called“transition channels”, as shown in FIG. 22, be reserved for single-modeterminals. The single-mode terminals preferably use transition channelswhile inside base station coverage. It is also preferred that dual-modeterminals also use the transition channels under certain circumstances,as will be described in detail herein.

As shown in FIG. 21, when a user places a call at step 2102, the userterminal will request a traffic channel from the network. It ispreferred that, at step 2104, the network instruct the terminal to makea series of measurements. If the terminal is single-mode, as determinedat decision step 2106, it will, at step 2118, preferably scan satellitechannels for signal strength and interference. If interference levelsare acceptable, as determined at decision step 2116, and if a satellitechannel is available, as determined at decision step 2126, then theterminal will preferably be assigned that channel at step 2124. If asatellite channel is not available, the terminal will preferably retry afixed number of times, as determined at decision step 2128, startingfrom the measurements, before the call is determined to be unsuccessfulat step 2136. If interference levels are unacceptable, the terminal willpreferably request a transition channel at step 2114. If a transitionchannel is available, as determined at decision step 2112, then theterminal will preferably be assigned that channel at step 2110. If atransition channel is not available, the terminal will preferably retrya fixed number of times starting from the measurements, before the callis determined to be unsuccessful at step 2136.

If, as determined at decision step 2106, the terminal is dual-mode, itwill preferably scan both satellite and base station channels for signalstrength and interference at step 2108. If interference levels areunacceptable as determined at decision step 2122, the terminal willpreferably request a transition channel at step 2120. If a transitionchannel is available as determined at decision step 2132, then theterminal will preferably be assigned that channel at step 2134. If atransition channel is not available, the terminal will preferably retrya predetermined number of times, as determined at decision step 2130,starting from the measurements, before the call is determined to beunsuccessful at step 2136. If interference is acceptable, the terminalwill preferably request the system (i.e., satellite or base station)with the dominant signal, as determined at decision step 2140. If theterminal requests a satellite channel at step 2138, and one is availableas determined at decision step 2142, then the terminal will preferablybe assigned that channel at step 2144. If a satellite channel is notavailable, the terminal will preferably retry a fixed number of timesstarting from the measurements, as determined at decision step 2130,before the call is determined to be unsuccessful at step 2136. If theterminal requests a base station channel at step 2148, and one isavailable as determined at decision step 2146, then the terminal willpreferably be assigned that channel at step 2150. If a base stationchannel is not available, the terminal will preferably retry a fixednumber of times starting from the measurements, as determined atdecision step 2130, before the call is determined to be unsuccessful atstep 2136. It should be obvious to those skilled in the art that manyvariations of the FIG. 21 are available that would accomplish the callinitialization objective. For example, the specific sequence of stepsmay be altered or re-ordered, such that the overall functionality issubstantially the same or similar. For example, the determinationwhether the user is in dual-mode may be juxtaposed after measuringsatellite and base station channels.

FIG. 23 shows an exemplary method of satellite to base-stationproximity-initiated hand-off. As shown in FIG. 23, as a user terminalapproaches a base station at step 2302, it will preferably alert thenetwork of its proximity. If, as determined at decision step 2304, theterminal is single-mode, then one of two things can generally happen.If, for example, the single-mode terminal is being served by atransition channel, as determined at decision step 2312, then hand-offis not required 2310. If, for example, the single-mode terminal is beingserved by a satellite channel, then a request to hand-off to atransition channel is preferably made at step 2318. If a transitionchannel is available as determined at decision step 2318, then thehand-off procedure preferably takes place at step 2326. If a transitionchannel is not available, then the terminal preferably checks if itscurrent interference level is acceptable at decision step 2334. Ifinterference is acceptable, then the terminal preferably camps on thesatellite at step 2336, preferably for a pre-specified period of timebefore another request to hand-off to a transition channel is made. Ifinterference is not acceptable, the terminal preferably determines ifanother satellite channel is available for use at decision step 2346. Ifnot, then the terminal preferably camps on the channel at step 2336. Ifso, the terminal is preferably re-assigned to a new satellite channel atstep 2348, which it camps on at step 2336, preferably for apre-specified period of time before another request to hand-off to atransition channel is made at step 2318.

If the terminal is dual-mode, then a request to hand-off to a basestation channel is preferably made at step 2306. If, as determined atdecision step 2314, a base station channel is available, then thehand-off procedure preferably takes place at step 2308. If a basestation channel is not available, then a request to hand-off to atransition channel is preferably made at step 2320. If, as determined atdecision step 2330, a transition channel is not available, then theterminal preferably checks, at decision step 2340, if its currentinterference level is acceptable. If interference is acceptable, thenthe terminal preferably camps on the channel at step 2338, preferablyfor a pre-specified period of time before another request to hand-off toa base station channel is made at step 2306. If interference is notacceptable, the terminal preferably determines at decision step 2352, ifanother satellite channel is available for use. If not, then theterminal preferably camps on the satellite at step 2338. If so, theterminal is preferably re-assigned to a new satellite channel at step2350, which it preferably camps on for a pre-specified period of time atstep 2338 before another request to hand-off to a base station channelis made at step 2306.

If the first attempt to hand-off to a transition channel was successful,then the terminal preferably camps on this channel at step 2316,preferably for a pre-specified period of time before comparing thesignal levels of the transition channel and base station at decisionstep 2324. If the base station is not stronger by a pre-specifiedmargin, then the terminal preferably camps on the transition channel atstep 2316, preferably until the base station channel becomes thestronger channel. If the base station is stronger by a pre-specifiedmargin, then a request to hand-off to a base station channel ispreferably made at step 2332. If, as determined at decision step 2342, abase station channel is available, then the hand-off procedurepreferably takes place at step 2356. If a base station channel is notavailable, then the terminal preferably camps on the transition channelat step 2316 preferably for a pre-specified period of time beforecomparing the signal levels of the transition channel and base stationagain. It should be obvious to those skilled in the art that manyvariations of the FIG. 23 are available that would accomplish thesatellite to base station hand-off objective. For example, the specificsequence of steps may be altered or re-ordered, such that the overallfunctionality is substantially the same or similar.

FIG. 24 shows an exemplary method of base station-to-satellite and basestation-to-base station proximity-initiated hand-off. As shown in FIG.24 at step 2402, as a dual-mode terminal moves away from the basestation it is served by, it will eventually take appropriate measuresupon sensing a stronger channel, either from the satellite, another basestation, or a system or device associated therewith. If, as determinedat decision step 2404, a satellite channel is stronger than aneighboring base station channel, then a request to hand-off to asatellite channel is preferably made at step 2406. If, as determined atdecision step 2408, a satellite channel is available, then the hand-offprocedure preferably takes place at step 2410. If a satellite channel isnot available or if a neighboring base station channel is stronger thana satellite channel, then a request to hand-off to a base stationchannel is preferably made at step 2406. If, as determined at decisionstep 2414, a base station channel is available, then the hand-offprocedure preferably takes place at step 2410. If a base station channelis not available, then the terminal preferably camps on its currentchannel at step 2416, preferably for a pre-specified period of timebefore making measurement comparisons again at decision step 2404. Itshould be obvious to those skilled in the art that many variations ofFIG. 24 are available that would accomplish the basestation-to-satellite and base station-to-base station hand-offobjectives. For example, the specific sequence of steps may be alteredor re-ordered, such that the overall functionality is substantially thesame or similar.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention. While the foregoinginvention has been described in detail by way of illustration andexample of preferred embodiments, numerous modifications, substitutions,and alterations are possible without departing from the scope of theinvention defined in the following claims.

1. A method of assigning and/or reusing frequencies between one or morewireless communications systems, the method comprising: configuring, byat least one satellite, a first satellite spot beam having a first setof frequencies associated therewith and providing satellite-basedcommunications; configuring, by at least one satellite, a secondsatellite spot beam having a second set of frequencies associatedtherewith and providing satellite-based communications; configuring, byat least one base station, at least one terrestrial cell that at leastpartially overlaps geographically with the first satellite spot beamhaving a third set of frequencies associated therewith and providingterrestrial communications; and assigning to, allowing reuse by and/orallowing borrowing by, the at least one terrestrial cell, at least aportion of the first set of frequencies and/or at least a portion of thesecond set of frequencies responsive to at least one predeterminedcriterion that is based on at least a relative capacity between thefirst and second satellite spot beams.
 2. The method of claim 1 whereinthe assigning to, allowing reuse by and/or allowing borrowing by ispreferentially performed relative to the second set of frequencies. 3.The method of claim 1 wherein the satellite-based communications areprovided using a satellite air-interface protocol and the terrestrialcommunications are provided using a terrestrial air-interface protocol.4. The method of claim 3 wherein the satellite air-interface protocol isdifferent compared to the terrestrial air-interface protocol.
 5. Themethod of claim 3 wherein the satellite air-interface protocol is basedon a terrestrial air-interface protocol.
 6. The method of claim 1wherein the at least one predetermined criterion comprises: a criterionthat selects frequencies from one of a plurality of satellite spot beamsthat are equidistant from the at least one terrestrial cell, based uponrelative capacities of the plurality of satellite spot beams; acriterion that selects frequencies from one of a plurality of satellitespot beams that is closer to the at least one terrestrial cell thananother of the plurality of spot beams, based upon relative capacitiesof the one and the another of the plurality of spot beams; and/or acriterion that selects frequencies from a satellite spot beam that isdirectly adjacent the first satellite spot beam, based upon capacity ofthe satellite spot beam that is directly adjacent the first satellitespot beam relative to the second satellite spot beam.
 7. A method ofassigning and/or reusing frequencies between one or more communicationssystems, the method comprising: configuring, by at least one satellite,a first satellite spot beam having a first set of frequencies associatedtherewith; configuring, by at least one satellite, a second satellitespot beam having a second set of frequencies associated therewith;configuring, by at least one base station, at least one terrestrial cellthat at least partially overlaps geographically with the first satellitespot beam having a third set of frequencies associated therewith; andassigning to, allowing reuse by and/or allowing borrowing by, the firstand/or second satellite spot beam(s), at least a portion of the thirdset of frequencies responsive to at least one predetermined criterionthat is based on at least a relative capacity between the first andsecond satellite spot beams.
 8. The method of claim 7 wherein the atleast one predetermined criterion comprises: a criterion that selectsfrequencies from one of a plurality of satellite spot beams that areequidistant from the at least one terrestrial cell, based upon relativecapacities of the plurality of satellite spot beams; a criterion thatselects frequencies from one of a plurality of satellite spot beams thatis closer to the at least one terrestrial cell than another of theplurality of spot beams, based upon relative capacities of the one andthe another of the plurality of spot beams; and/or a criterion thatselects frequencies from a satellite spot beam that is directly adjacentthe first satellite spot beam, based upon capacity of the satellite spotbeam that is directly adjacent the first satellite spot beam relative tothe second satellite spot beam.
 9. A method of assigning and/or reusingfrequencies between one or more communications systems, the methodcomprising: configuring, by at least one satellite, a first satellitespot beam having a first set of frequencies associated therewith;configuring, by at least one satellite, a second satellite spot beamhaving a second set of frequencies associated therewith; configuring, byat least one base station, at least one terrestrial cell that at leastpartially overlaps geographically with the first satellite spot beamhaving a third set of frequencies associated therewith; and assigningto, allowing reuse by and/or allowing borrowing by, the at least oneterrestrial cell, at least a portion of the second set of frequenciesand/or at least a portion of the first set of frequencies, responsive toat least one predetermined criterion that is based on at least arelative capacity between the first and second satellite spot beams. 10.The method of claim 9 wherein the at least one predetermined criterioncomprises: a criterion that selects frequencies from one of a pluralityof satellite spot beams that are equidistant from the at least oneterrestrial cell, based upon relative capacities of the plurality ofsatellite spot beams; a criterion that selects frequencies from one of aplurality of satellite spot beams that is closer to the at least oneterrestrial cell than another of the plurality of spot beams, based uponrelative capacities of the one and the another of the plurality of spotbeams; and/or a criterion that selects frequencies from a satellite spotbeam that is directly adjacent the first satellite spot beam, based uponcapacity of the satellite spot beam that is directly adjacent the firstsatellite spot beam relative to the second satellite spot beam.
 11. Asystem for assigning and/or reusing frequencies between one or morewireless communications systems, the wireless communications systemscomprising at least one satellite capable of configuring a first spotbeam having a first set of frequencies associated therewith andproviding satellite-based communications, the at least one satellitealso capable of configuring at least one second spot beam having asecond set of frequencies associated therewith and providingsatellite-based communications, a terrestrial base station positionedwithin the first spot beam for configuring at least one terrestrialcell, the at least one terrestrial cell having a third set offrequencies associated therewith and providing terrestrialcommunications over a geographic coverage area that at least partiallyoverlaps with a geographic coverage area associated with the first spotbeam, and a first subscriber terminal positioned within the terrestrialbase station coverage area; the system for assigning and/or reusingfrequencies comprising: a controller that is configured to assign to,allow reuse by and/or allow borrowing by, the terrestrial base station,and/or for use by the first subscriber terminal in communicating with atleast one second subscriber terminal and/or other communicationsdevice(s), at least a portion of the second set of frequencies and/or atleast a portion of the first set of frequencies, responsive to at leastone predetermined criterion that is based on at least a relativecapacity between the first and second satellite spot beams.
 12. Thesystem of claim 11 wherein the assigning to, allowing reuse by and/orallowing borrowing by is preferentially performed relative to the secondset of frequencies.
 13. The system of claim 11 wherein thesatellite-based communications are provided using a satelliteair-interface protocol and the terrestrial communications are providedusing a terrestrial air-interface protocol.
 14. The system of claim 13wherein the satellite air-interface protocol is different compared tothe terrestrial air-interface protocol.
 15. The system of claim 13wherein the satellite air-interface protocol is based on a terrestrialair-interface protocol.
 16. The system of claim 11 wherein the at leastone predetermined criterion comprises: a criterion that selectsfrequencies from one of a plurality of satellite spot beams that areequidistant from the at least one terrestrial cell, based upon relativecapacities of the plurality of satellite spot beams; a criterion thatselects frequencies from one of a plurality of satellite spot beams thatis closer to the at least one terrestrial cell than another of theplurality of spot beams, based upon relative capacities of the one andthe another of the plurality of spot beams; and/or a criterion thatselects frequencies from a satellite spot beam that is directly adjacentthe first satellite spot beam, based upon capacity of the satellite spotbeam that is directly adjacent the first satellite spot beam relative tothe second satellite spot beam.
 17. A system for assigning and/orreusing frequencies between a satellite and a terrestrial base station;wherein the satellite is configured to provide communications service toa first communications area having a first set of frequencies associatedtherewith and to at least one second communications area having a secondset of frequencies associated therewith; and wherein the terrestrialbase station is positioned within the first communications area and isconfigured to provide communications service to at least one thirdcommunications area having at least partially overlapping geographiccoverage with the first communications area, the third communicationsarea having a third set of frequencies associated therewith; the systemfor assigning and/or reusing frequencies comprising: a networkoperations controller that assigns to, allows reuse by and/or allowsborrowing by, the terrestrial base station, at least a portion of thesecond set of frequencies and/or at least a portion of the first set offrequencies responsive to at least one predetermined criterion that isbased on at least a relative capacity between the first and secondcommunications areas.
 18. The system of claim 17 wherein the at leastone predetermined criterion comprises: a criterion that selectsfrequencies from one of a plurality of communications areas that areequidistant from the at least one third communications area, based uponrelative capacities of the plurality of communications areas; acriterion that selects frequencies from one of a plurality ofcommunications areas that is closer to the at least one thirdcommunications area than another of the plurality of communicationsareas, based on relative capacities of the one and the another of theplurality of communications areas; and/or a criterion that selectsfrequencies from a communications area that is directly adjacent thefirst communications area based upon capacity of the communications areathat is directly adjacent the first communications area relative to thesecond communications area.
 19. A system for assigning and/or reusingfrequencies between a plurality of communications systems, wherein theplurality of communications systems comprises at least one satellitecapable of configuring a first satellite spot beam having a first set offrequencies associated therewith; the at least one satellite alsocapable of configuring at least one second satellite spot beam having asecond set of frequencies associated therewith; and a terrestrial basestation positioned within the first satellite spot beam for configuringat least one terrestrial cell having a third set of frequenciesassociated therewith and having an area of geographic coverage that isat least partially overlapping geographically with an area of geographiccoverage associated with the first satellite spot beam; the system forassigning and/or reusing frequencies comprising: a network operationscontroller for assigning to, allowing reuse by and/or allowing borrowingby, the at least one second and/or first satellite spot beam(s), atleast a portion of the third set of frequencies responsive to at leastone predetermined criterion that is based on at least a relativecapacity between the first and second satellite spot beams.
 20. Thesystem of claim 19 wherein the at least one predetermined criterioncomprises: a criterion that selects frequencies from one of a pluralityof satellite spot beams that are equidistant from the at least oneterrestrial cell, based upon relative capacities of the plurality ofsatellite spot beams; a criterion that selects frequencies from one of aplurality of satellite spot beams that is closer to the at least oneterrestrial cell than another of the plurality of spot beams, based uponrelative capacities of the one and the another of the plurality of spotbeams; and/or a criterion that selects frequencies from a satellite spotbeam that is directly adjacent the first satellite spot beam, based uponcapacity of the satellite spot beam that is directly adjacent the firstsatellite spot beam relative to the second satellite spot beam.
 21. Asystem for assigning and/or reusing frequencies between a plurality ofcommunications systems, the system for assigning and/or reusingfrequencies comprising: at least one satellite capable of configuring afirst satellite spot beam having a first set of frequencies associatedtherewith; the at least one satellite also capable of configuring atleast one second satellite spot beam having a second set of frequenciesassociated therewith; a terrestrial base station positioned within thefirst satellite spot beam for configuring at least one terrestrial cell,the terrestrial cell having a third set of frequencies associatedtherewith and having an area of geographic coverage at least partiallyoverlapping with an area of geographic coverage of the first satellitespot beam; and a network operations controller for assigning to,allowing reuse by and/or allowing borrowing by, the terrestrial basestation at least a portion of the second set of frequencies and/or atleast a portion of the first set of frequencies, responsive to at leastone predetermined criterion that is based on at least a relativecapacity between the first and second satellite spot beams.
 22. Thesystem of claim 21 wherein the at least one predetermined criterioncomprises: a criterion that selects frequencies from one of a pluralityof satellite spot beams that are equidistant from the at least oneterrestrial cell, based upon relative capacities of the plurality ofsatellite spot beams; a criterion that selects frequencies from one of aplurality of satellite spot beams that is closer to the at least oneterrestrial cell than another of the plurality of spot beams, based uponrelative capacities of the one and the another of the plurality of spotbeams; and/or a criterion that selects frequencies from a satellite spotbeam that is directly adjacent the first satellite spot beam, based uponcapacity of the satellite spot beam that is directly adjacent the firstsatellite spot beam relative to the second satellite spot beam.
 23. Asystem for assigning and/or reusing frequencies between a plurality ofcommunications systems; the plurality of communications systemscomprising at least one satellite capable of configuring a firstsatellite spot beam having a first set of frequencies associatedtherewith; the at least one satellite also capable of configuring atleast one second satellite spot beam having a second set of frequenciesassociated therewith, the system for assigning and/or reusingfrequencies comprising: a terrestrial base station positioned within thefirst satellite spot beam for configuring at least one terrestrial cell,the at least one terrestrial cell having a third set of frequenciesassociated therewith and having an area of geographic coverage at leastpartially overlapping with an area of geographic coverage associatedwith the first satellite spot beam; and a network controller forassigning to, allowing reuse by and/or allowing borrowing by, theterrestrial base station at least a portion of the second set offrequencies and/or at least a portion of the first set of frequencies,responsive to at least one predetermined criterion that is based on atleast a relative capacity between the first and second satellite spotbeams.
 24. The system of claim 23 wherein the at least one predeterminedcriterion comprises: a criterion that selects frequencies from one of aplurality of satellite spot beams that are equidistant from the at leastone terrestrial cell, based upon relative capacities of the plurality ofsatellite spot beams; a criterion that selects frequencies from one of aplurality of satellite spot beams that is closer to the at least oneterrestrial cell than another of the plurality of spot beams, based uponrelative capacities of the one and the another of the plurality of spotbeams; and/or a criterion that selects frequencies from a satellite spotbeam that is directly adjacent the first satellite spot beam, based uponcapacity of the satellite spot beam that is directly adjacent the firstsatellite spot beam relative to the second satellite spot beam.
 25. Amethod of assigning and/or reusing frequencies between one or morecommunications systems, the one or more communications systemscomprising at least one satellite capable of configuring a firstsatellite spot beam having a first set of frequencies associatedtherewith and at least one second satellite spot beam having a secondset of frequencies associated therewith; the method comprising:configuring, by at least one base station, at least one terrestrial cellwithin the first satellite spot beam having a third set of frequenciesassociated therewith and having at least partially overlappinggeographic coverage with the first satellite spot beam; and assigningto, allowing reuse by and/or allowing borrowing by, the at least oneterrestrial cell, at least a portion of the second set of frequenciesand/or at least a portion of the first set of frequencies, responsive toat least one predetermined criterion that is based on at least arelative capacity between the first and second satellite spot beams. 26.The method of claim 25 wherein the assigning to, allowing reuse byand/or allowing borrowing by is preferentially performed relative to thesecond set of frequencies.
 27. The method of claim 25 furthercomprising: configuring at least one second terrestrial cell within theat least one second satellite spot beam having a fourth set offrequencies associated therewith and having at least partiallyoverlapping geographic coverage with the at least one second satellitespot beam; and assigning to, allowing reuse by and/or allowing borrowingby, the at least one second terrestrial cell, at least a portion of thefirst set of frequencies and/or at least a portion of the second set offrequencies, responsive to at least one predetermined criterionassociated at least with a capacity requirement.
 28. The method of claim27 wherein the assigning to, allowing reuse by and/or allowing borrowingby is preferentially performed relative to the first set of frequencies.29. The system of claim 25 wherein the at least one predeterminedcriterion comprises: a criterion that selects frequencies from one of aplurality of satellite spot beams that are equidistant from the at leastone terrestrial cell, based upon relative capacities of the plurality ofsatellite spot beams; a criterion that selects frequencies from one of aplurality of satellite spot beams that is closer to the at least oneterrestrial cell than another of the plurality of spot beams, based uponrelative capacities of the one and the another of the plurality of spotbeams; and/or a criterion that selects frequencies from a satellite spotbeam that is directly adjacent the first satellite spot beam, based uponcapacity of the satellite spot beam that is directly adjacent the firstsatellite spot beam relative to the second satellite spot beam.